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500 Miles - IT'S PARTY TIME!!!! Two acceleration runs with my CT5-V Blackwing six-speed!!

Daijoubu

Seasoned Member
Joined
Jul 3, 2021
Messages
112
Location
Charlotte, NC
Think he was commenting on the difference in units for one pressure above ambient and one below.
I was. Thought it odd to see a boost gauge in in.Hg until it switched over to positive boost and showed PSI. I got curious and looked around to see that analog boost gauges are generally, in fact, in.Hg below 0 (vacuum) and PSI above 0 (boost).
 

Mirza Grebovic

Seasoned Member
Joined
Mar 13, 2021
Messages
373
Location
Michigan
V-Series Cadillac(s)?
2022 CT4-V Blackwing
Reply to post before yours above. I understand but thats a proper boost gauge, psi is not how you measure vacuum. Boost you do measure in psi/bar.
 

Ryan

Seasoned Member
Joined
Apr 2, 2021
Messages
77
Location
Midwest
Reply to post before yours above. I understand but thats a proper boost gauge, psi is not how you measure vacuum. Boost you do measure in psi/bar.
The actual answer to this question is kind of a historical convenience thing. When you’re working near true vacuum pressures, you end up with psi readings of 0.0003 or stupid things like that, vs 1 or 2 inches of Hg. Engineers don’t like lots of zeroes on their units, because it leads to human transcription errors. So space applications and good vacuum pumps led to inches of Mercury, and the standard stuck.

I don’t think it makes a lot of sense when we are never pulling that hard of a vacuum in a car, but history wins!
 

Daijoubu

Seasoned Member
Joined
Jul 3, 2021
Messages
112
Location
Charlotte, NC
The actual answer to this question is kind of a historical convenience thing. When you’re working near true vacuum pressures, you end up with psi readings of 0.0003 or stupid things like that, vs 1 or 2 inches of Hg. Engineers don’t like lots of zeroes on their units, because it leads to human transcription errors. So space applications and good vacuum pumps led to inches of Mercury, and the standard stuck.

I don’t think it makes a lot of sense when we are never pulling that hard of a vacuum in a car, but history wins!
There's always a reason for weird stuff like this, thanks for the info. Lots of "standards" for measuring pressure. I see hPa and bar used a lot as well.
 

WONT TAP

Active Member
Joined
Jul 24, 2021
Messages
43
Location
Columbus OH
V-Series Cadillac(s)?
2016 ATS-V A8, 2018 ATS-V M6, 2022 CT4-V Blackwing A10
Anyway, does GM still mispell the word gage, or is it gauge now?
Neither gage nor gauge is a misspelling. Both are correct.

However, 'mispell' is a common mistake. :p
 

Daijoubu

Seasoned Member
Joined
Jul 3, 2021
Messages
112
Location
Charlotte, NC
Neither gage nor gauge is a misspelling. Both are correct.

However, 'mispell' is a common mistake. :p
Ha, I was wondering what that red squiggly line under mispell was. Anyway, for the longest time GM used the word "gage" everywhere, but they seem to have changed to the more common "gauge". I wonder why they changed?
 

SSEEYA

Seasoned Member
Joined
Jun 3, 2021
Messages
180
Location
Utah
Check out my video below. It shows the transition of the tachometer at 500 miles to allowing the normal, full 6,500rpm rev range.

Have I mentioned yet, I absolutely love this car?!?!?!

Watch this video to the end. I get a nice, clean 0-151mph run!


I just hit the 500 mile mark and did a similar pull (40-120ish). I've done a couple of pulls since as well. I can only get to 8 lbs. of boost. I see you hit 9 easily and 10 as well.

What would cause me to only get 8 lbs? My best 0-60 so far is 4.4 with a relatively soft launch and a bit of an early 1-2 shift. I can't see any chance of getting sub 3.8. Is it just the altitude? I'm at like 4700 ft. Any ideas?
 

CT4-V Blackwing

Seasoned Member
Joined
Feb 17, 2021
Messages
1,335
Location
California
V-Series Cadillac(s)?
2022 CT4-V Blackwing
I just hit the 500 mile mark and did a similar pull (40-120ish). I've done a couple of pulls since as well. I can only get to 8 lbs. of boost. I see you hit 9 easily and 10 as well.

What would cause me to only get 8 lbs? My best 0-60 so far is 4.4 with a relatively soft launch and a bit of an early 1-2 shift. I can't see any chance of getting sub 3.8. Is it just the altitude? I'm at like 4700 ft. Any ideas?
Possibly an air pocket in the intercooler system that needs to be bled out?
 

quikag

Seasoned Member
Joined
Jul 27, 2021
Messages
85
Location
Dallas
V-Series Cadillac(s)?
2022 CT5-V Blackwing
I just hit the 500 mile mark and did a similar pull (40-120ish). I've done a couple of pulls since as well. I can only get to 8 lbs. of boost. I see you hit 9 easily and 10 as well.

What would cause me to only get 8 lbs? My best 0-60 so far is 4.4 with a relatively soft launch and a bit of an early 1-2 shift. I can't see any chance of getting sub 3.8. Is it just the altitude? I'm at like 4700 ft. Any ideas?
Higher altitude will result in less boost from a supercharged application all things equal. I'm a CPA, so I can't give you a technical answer, but it is a real thing. :D
 

RupertH

Seasoned Member
Joined
Feb 23, 2021
Messages
138
Location
Las Vegas, NV
V-Series Cadillac(s)?
Hopeful...
Here's a graph of atmospheric pressure over elevation. It's not the whole story, because the pressure drop is not as smooth at the surface (i.e., on the ground in Denver at ~5,000 feet will not be the same as 5,000 feet in the air over the ocean) and the temperature and humidity also play a role.
1632158736105.png


Bottom line, density altitude is probably what really matters- and on a hot, humid, summer day in the mountain west can easily exceed 7500' in places that are only physically 3-4,000' above sea level.
 

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